Stacked Icons

fa-phone on fa-square-o
fa-phone on fa-circle
fa-phonel on fa-square
fa-ban on fa-phone

To stack multiple icons, use the fa-stack class on the parent, the fa-stack-1x
for the regularly sized icon, and fa-stack-2x for the larger icon. fa-inverse
can be used as an alternative icon color. You can even throw larger icon classes on the parent
to get further control of sizing.